Modern Pb-acid storage batteries utilize Faure-type electrode plates which comprise a conductive grid embedded in a leady active material. The plates are formed by pasting the grid with various proprietary mixes comprising principally PbO and then electrochemically converting the PbO to Pb and PbO.sub.2 for the negative and positive electrodes respectively. The grid can take many forms depending on the manufacturer but generally comprises a network of criss-crossing interconnected grid wires depending from a current collecting upper border. The grid may or may not include other borders at its sides and bottom edges. The active material is retained in the grid primarily in the interstitial openings defined by the several grid wires making up the network.
A battery's capacity is usually rated by how many ampere hours it will deliver at a certain discharge rate before its terminal voltage falls below a predetermined value (i.e. the cutoff voltage). When the terminal voltage falls below this cutoff voltage, the battery is said to be completely discharged though, in fact, a considerable amount of unreacted active material remains in the plates. The ratio of the active material reacted to the amount of active material originally present is the utilization efficiency (often called "coefficient of use") of the active material. Typically, the remaining unreacted active material (i.e. on a total plate basis) exceeds the reacted material at the end of discharge. Hence utilization efficiencies of less than about 50% are common.
The active material utilization efficiency of a lead-acid battery plate actually varies across the face of the plate. The active material nearer the grid wires, for example, is utilized more efficiently than the active material in the center of the grid openings defined by the grid wires. This phenomenon is apparently due, at least in part, to the IR drop between the center of the opening and the surrounding grid wires.
Whatever the reason, it has been demonstrated that the active material at the center of the grid opening is less efficiently utilized than the active material proximate the grid wires. This excess of unreacted active material at the center of the opening merely contributes to the weight of the battery without providing any benefit in return.
It is an object of the present invention to provide a lead-acid storage battery plate having an active material distribution which contributes to a more efficient utilization of the active material and accordingly yields lighter weight plates having comparable capacity to uniformly thick plates of greater weight or same-weight plates having increased capacity. It is a further object of the present invention to provide such storage battery plates with increased surface area and improved electrolyte accessibility for improved voltage potential under load. It is a still further object of the present invention to provide a process for redistributing the active material on a previously pasted lead-acid storage battery plate to achieve the aforesaid improved utilization efficiency and voltage.